1. Field of the Invention
The present invention relates to a turbocharger control system for controlling a turbocharger including an electric motor mounted on a rotatable shaft which interconnects a turbine and a compressor, so that a motor vehicle incorporating the turbocharger can quickly be re-accelerated after the motor vehicle has been subjected to engine braking.
2. Description of the Prior Art
There are well known turbochargers which introduce exhaust gases from an engine to an exhaust turbine to rotate the turbine at a high speed, and pressurize intake air with a compressor directly coupled to the exhaust turbine for thereby supercharging the engine. Japanese Laid-Open Patent Publication No. 60-195329 discloses an apparatus in which a rotary electric machine is mounted on the rotatable shaft of such a turbocharger and operable as an electric motor or generator depending on the operating condition of the engine. At least when the engine operates at a low speed and under a high load, the rotary electric machine is operated as the motor or the generator to drive the compressor for supercharging the engine.
According to the disclosed apparatus, since the supercharging operation of the compressor is assisted by the rotary electric machine operating as the motor during the low-speed, high-load operation of the engine, the boost pressure is increased and the torque produced by the engine is increased.
However, when the engine needs to be accelerated quickly, even if the motor is energized to increase the boost pressure, the boost pressure cannot be increased as quickly as it is desired to accelerate the engine since the rotational parts such as the motor and the compressor have moments of inertia and it takes time to compress air.